Square Foot Vegetable Gardening Using Timber Raised Beds

What is Square Foot Gardening?Square foot gardening is a method of growing vegetables which centers around planting crops in blocks rather than rows. The system divides the growing space up into a grid of square foot areas (hence the name), with each one crop allocated to each square. The numbers of each crop planted in the square varies depending the space each one needs, for example one square foot will fit 16 carrots yet only one large cabbage.

The term ‘Square Foot Gardening’ comes form a book written in the 1970’s (and updated and re-published ever since) by ex engineer Mel Bartholomew. Mr.Bartholomew questions the practice of growing in rows and maintains far more produce can be grown in smaller spaces by using raised vegetable beds and his square foot grid system. The book claims that the same yields can be achieved using 80% less space than conventional systems which, especially for urban growing, has to be good news, right?

As a conventional grower I’d have to say was a bit dubious about some of the books claims, the growing space just seems so small to give adequate nutrition to such close planted crops. The system does rely on using a very fertile soil mix (not chemical fertilizers) made up of a peat base, garden compost and vermiculite but even with the very best compost the number of plants competing in such a small space will result in some casualties.

I would suggest using a deeper bed than the 6 inches recommended in the book to give you a greater depth of soil to make a more versatile bed. The Square Foot Gardening book recommends using height extensions on the squares used for deeper rooted crops but this seems cumbersome especially when you take crop rotation into account. It seems to make more sense to use a deeper bed from the outset which will give you more flexibility in your planting plans.

In general I’d say SFG is a very good system for beginners, especially if you avoid many of the larger crops like cabbage or broccoli (which aren’t really suitable for small spaces anyway) and focus on a broad range of leafy crops like salads, spinach and chard and close planted crops like radish, carrot and beetroot.

Square Foot Gardening – An excellent system for beginners.There’s no real difference in square foot and raised bed gardening other than the placement of the plants, both require boxes of soil/compost mix placed above the ground but the square foot system is a lot easier for a novice to understand.

One of the biggest problems novice vegetable growers have are the planting distances of the various crops. In the traditional system we have a distance between plants and a distance between rows which can make it difficult to plan a garden, especially in a small space. The fact that square foot gardening revolves around a fixed measurement of one square foot makes the system very easy to use, all you need to know is how many plants fit in that square.

A typical Square Foot Garden uses timber raised beds 6-8 inches high and 4ft square. The 4ft bed is then subdivided using string or timber laths to form a grid of 16 squares. Each square is filled with with the plants of your choice according to the recommended numbers for each square foot. The grid system keeps everything nice and ordered both in your garden and in your mind which is helpful for someone trying to get to grips with a subject like vegetable growing.

I’m not saying Square Foot Gardening doesn’t have its flaws (I believe it does, which I’ll go into later), I’m just saying it’s a very good place to start. I expect once a first time grower gains more experience they will diversify into other methods of which SFG will play a part but like any ‘one size fits all’ solution it can’t tick all the boxes but it does tick some of them very well.

Timber Raised Beds For Square Foot Gardening.
The most important components of the Square Foot Gardening technique is the use of raised beds to contain the soil or compost. Raised vegetable beds are essentially boxes of soil mix, the idea being you should be able to grow anywhere as the fertility is in the box rather than the surrounding soil. The benefit for a beginner is you only need to concentrate on creating and maintaining a fertile mix in a small concentrated area rather than tackling a large vegetable plot.

As with all raised bed growing you never walk on the soil in the bed which stops it becoming compacted and helps keep it ‘open’ and aerated for easy root penetration. A light, friable soil is better for your plants and much easier for you to work on with seeds easily sown, seedlings easily planted and weeds easily pulled!

The SFG book recommends using 4ft square beds 6 inches high. The beds can be placed on a hard surface if required and don’t require any soil, just the recommended compost mix. In my (humble) opinion, I think you will need a greater depth of soil for your beds, here’s my reasons:

Square Foot Gardening relies on plants being grown in very close proximity to achieve worthwhile yields from such a small space. Your soil will need to be well fed to support such intensive growing so a greater volume of good soil will give better fed crops.

Raised beds require watering, the best vegetable are grown with an even irrigation regime. A deeper raised bed with a larger volume of soil won’t dry out as quickly.

A higher bed is easier to work meaning you are more likely to look after it. If you’re starting something new, make it easy on yourself.

A taller bed looks so much better, after all if you’re trying to grow vegetables in a small space it’s likely to be in your precious back garden or yard right? Make sure it looks good.

If your Square Foot Garden is being placed on garden soil or grass a 9 inch high raised bed would be sufficient as the roots of your plants will be able to grow into the soil below the bed. I don’t recommend a weed control membrane between the beds and the soil as you want to encourage earthworms up into the soil mix as they help to keep it aerated and fertilized.

Square Foot Gardening Compost MixThis is where we enter a bit of a grey area with the SFG guidelines and where I think a bit of tinkering is required. The recommended mix, known as ‘Mel’s Mix’ is comprised of the following:

1/3 moss peatThe peat compost is a base and shouldn’t be seen as carrying any nutrients. If you are using multipurpose peat compost be aware that any added nutrients whether man made or organic will only last about 4 weeks. After that you will need to feed your plants. Many gardeners still use peat composts but it’s increasingly frowned upon because peat harvesting destroys natural habitats. There is a good range of peat free alternatives now available like ‘New Horizon’ peat free compost.

1/3 garden compostBy garden compost I mean composted material which has been broken down to a crumbly soil like consistency, I don’t mean peat. This includes composted green waste either from your garden of available commercially. Mel recommends buying compost bags from a number of different sources to make sure you achieve a broad spread of nutrients. It seems (anyone from the States please help me) that compost in the US refers to composted animal manure also so it’s difficult to know exactly what he’s advising here.

1/3 VermiculiteVermiculite is used to hold water in the compost and helps keep the mix light and open. It also has the advantage, because of it’s water holding properties, of absorbing and storing soluble nutrients which are then slowly released back to your plants. Vermiculite is more commonly used in potting mixes and can be expensive to use on a larger scale.

What’s the problem?The problem I have is the most important bit is the compost, after all that’s what’s feeding your plants and with the high demands of the plants in such a tight spacing you’re asking an awful lot of it. The plants still need the same building blocks to produce food but have less root space to do it in so the fertility of your soil is hugely important. If you’re not making your own you will need to buy in a municipal compost but even the best you’ll get (quality varies greatly) will need a nitrogen boost to support such intensive vegetable growing.

What’s the answer?We find the very best compost for slow release feeding of Square Foot vegetable beds is our ‘Envirogrind’ soil improver. It is a rich, dark compost made from properly composted green waste mixed with 25% composted fish waste. It is an excellent soil improver but also the ideal supplement for a square foot garden mix. I have been to the facility where it is produced and can tell you it is made by pumping air through the compost 24 hours a day resulting in the best textured finished product I have ever seen.

As I’ve said in the raised bed section increasing the bulk of soil will help but I would also recommend using a natural slow release feed to avoid disappointing yields. The best product I have come across is ‘Seamungus’ seaweed and poultry manure pellets which give plenty of nitrogen from the manure plus a whole host of minerals and trace elements from the seaweed.

You will need a base like moss peat for your beds but I would recommend a substitute peat free version (usually made from composted bark and waste timber) or a coco peat (made from coconut husks) compost.

I’m not sure how necessary the vermiculite is and may be more important in more arid climates where beds dry out quickly. If you are trying a single 4ft by 4ft bed it might be worth a trial but I suspect in the UK and Ireland it may not be necessary.